The present invention is generally directed to a system and method for effecting uterine contractions of an animal. The present invention is more particularly directed to such a system and method for detecting and automatically stimulating contractions of the uterus of a human.
Prolonged pregnancy, generally classified as a gestational age exceeding 42 weeks of gestation, is associated with increased perinatal morbidity and mortality. Specifically, in addition to the increased neonatal deaths, there is an increase in the meconium aspiration, depressed infant at five minutes, and cesarean section rate. The mortality from meconium aspiration can be as high as 38% for those women managed expectantly.
Electrical energy applied to the myometrium or uterine muscle has been proposed to affect uterine contractions. One system and method to this end is disclosed in Karsdon, U.S. Pat. Nos. 5,447,526 and 5,713,940 which are incorporated herein by reference. In accordance with a preferred embodiment disclosed in these patents, a first or positive electrode is placed in surface contact to a woman's abdomen over the top of the uterus. Four negative electrodes are placed in spaced apart relation in surface contact to the woman's abdomen over lower portions of the uterus beginning at approximately a mid portion of the uterus. The negative electrodes and the positive electrode are then connected to a muscle controller which generates square wave pulse trains of current between the positive electrode and the negative electrodes. The muscle controller is capable of providing current pulse trains of selectable polarity. The controller is activated to inhibit uterine contractions when they are undesirably present or to initiate uterine contractions when they are undesirably absent.
In accordance with a further embodiment disclosed in the above-referenced Karsdon patents, a uterine contraction monitor is added to the system with feedback to the controller. The monitor is disposed for surface contact with the abdomen. The amount of electrical energy applied is thus responsive to the sensed contractions. The feedback may be negative or positive depending upon whether contraction initiation or inhibition is desired.
While the contraction monitor of Karsdon represents a significant step forward in the prenatal management of patients, there remains substantial room for improvement. The contraction monitor disclosed in the Karsdon patents is a surface monitor. Such monitors respond to physical movement.
As a result, physical movement which is a certainty to occur other than that of real contractions will also be sensed and create a noisy signal environment in which the contraction affecting device must respond. It would be most advantageous to have a contraction monitor which is substantially more specific in detecting uterine contractions.
Further, surface monitors must be worn in order to function. Hence, if a patient is to be constantly monitored, the monitor must be worn at all times. This would include times of sleep and other times when such use would either be inconvenient, cumbersome, or confining.
In addition, there is no guarantee that such a surface monitor will remain in the same place or that if removed, it will be returned to the same location on the body at a later time. This can result in signals which are variable in amplitude and other characteristics making the application of threshold criterion difficult.
Hence, there is a need in the art for an improved uterine contraction detection and stimulation system to initiate uterine contractions. More specifically, such a system must be capable of providing detection signals of good quality, in a low noise environment, and specific to uterine contractions. This would assure that stimulation to initiate uterine contractions will be provided when actually needed and not be provided when such stimulation is not required. The present invention provides such an improved uterine contraction detection and stimulation system.